Some observations on phytoplankton species composition, biomass, and productivity in kenepuru sound, new zealand, 1982–83

Abstract

Phytoplankton species composition, biomass, and rates of primary production were determined at two sites within Kenepuru Sound, New Zealand, in spring, summer, and autumn of 1982–83. Microflagellates and ultraplankton (< 5–10 μm) were numerically very abundant on each occasion and small gymnodinoid nanno‐planktonic (< 10–15 μm) dinoflagellates were likewise always a common component of the populations. The dinoflagellate, Prorocentrum gracile, made a substantial contribution to the total biomass in summer. The diatom community changed from mainly small chain forming species (Chaetoceros spp., Leptocylindricus spp.) in spring to small solitary centric and pennate forms (Nitzchia longissima, Coscinodiscus spp.) in summer, to a diversity of larger taxa (Coscinodiscus concinnus, Eucampia zoodiacus) in autumn. The autotrophic ciliate Mesodinium rubrum was a particularly important member of the autumn photo‐autotrophic assemblage. Both phytoplankton biomass and productivity increased from spring to autumn. In situ rates of primary production ranged from 15 to 1420 mgC m‐2h‐1and chlorophyll a concentrations ranged from 6.9 to 258.5 mgChl a m‐2. A gross primary production rate, in summer, was estimated at 0.57 gC m‐2d‐1. Phytoplankton production and biomass appeared to be related to dissolved inorganic nutrient concentrations as a result of variations in the freshwater inflow. A tentative comparison between the rates of phytoplankton and cultivated mussel production is made. © Crown 1986.